1. Field of the Invention
The present invention relates to an air passage opening/closing system for opening and closing an air passage by moving a flexible film door having a plurality of door opening portions. The air passage opening/closing system is suitable for various equipments such as an air conditioning apparatus.
2. Related Art
As shown in FIG. 8, JP-A-64-85809 proposes an air passage opening/closing system applied to an automotive air conditioning apparatus. The air passage opening/closing system includes an air conditioning case (not shown) for forming an air passage. A driving shaft 101 and a driven shaft 102 are rotatably held in the air conditioning case. One end of a flexible film 104 having a plurality of film opening portions 103 is wound around the driving shaft 101 and the other end of the film 104 is wound around the driven shaft 102 to move the film 104 between the driving shaft 101 and the driven shaft 102.
Pulleys 105 and 106 are connected to longitudinal ends of the driving shaft 101 and the driven shaft 102 respectively in alignment. One end of a flexible wire 107 is wound on the pulley 105 and the other end of the wire 107 is wound on the pulley 106. The winding direction of the wire 107 is opposite to a winding direction of the film 104. An actuator 108 (e.g., electric motor) for driving the driving shaft 101 is connected to the driving shaft 101. When the actuator 108 rotates the driving shaft 101 forward and backward, the film 104 also moves forward and backward respectively.
When the driving shaft 101 rotates in a direction indicated by arrow A, the film 104 is wound around the driving shaft 101 to move in a forward direction (i.e., in a direction indicated by arrow B in FIG. 8). On the other hand, when the driving shaft 101 rotates in a direction opposite to the direction indicated by the arrow A, the film 104 is rewound around the driving shaft 101 and the wire 107 is wound around the pulley 105. Therefore, the driven shaft 102 rotates in a direction indicated by arrow C so that the film 104 is wound around the driven shaft 102 to move a backward direction (i.e., in a direction indicated by arrow D in FIG. 8).
The air conditioning case has a casing opening portion. When the film opening portions 103 match the casing opening portion while the film 104 moves forward and backward, the casing opening portion is opened. When the film opening portions 103 do not match the casing opening portion, the casing opening portion is closed. To prevent peripheral portions of the film opening portions 103 from being caught on a peripheral portion of the casing opening portion while the film 104 moves, each of the film opening portions 103 is formed in a hexagon shape in such a manner that a diagonal line connecting two sharper corners of each hexagon is parallel to the moving direction of the film 104.
However, as a result of studies and examinations of the air passage opening/closing system which has been produced experimentally, a harsh jarring noise having a high frequency about 9 kHz (hereinafter referred to as whistle noise) may sound when the casing opening portion starts opening. Because of the hexagon shape of each film opening portion 103, the width of each film opening portion 103 in a direction perpendicular to the moving direction of the film 104 decreases toward the ends of the film openings 103 in the moving direction. Thus, when the casing opening portion of the air conditioning case is starting to open by the casing opening portion of the film 104, an initial opened area of the casing opening portion is small as compared to a case where each film opening portion has a rectangular shape. That is, at the starting time for opening the casing opening portion, air flows from the casing opening portion with a very fast speed and may cause the whistle noise due to friction between air flowing from the casing opening portion and air outside the air conditioning case.